Connect the emitter
of transistor Q1 to the gate
of transistor Q2, input at the base of Q1, and probe at the collector
of Q2 (also tied to the collector of Q1). The result is like a normal transistor
, except that the effective beta
gain of base current to output current is equal to the product of the betas of the two transistors.
This is useful when you want a lot of impedance on your input to a system, or are dealing with high-current systems like voltage regulators. The drawbacks are that the base-emitter voltage is now 1.4 volts instead of the normal .7, and that the system is slower to turn off than a regular high-beta transistor.